Answer and Explanation:
Native american don't have any melodic hypothesis to give data with respect to their melodic traditions.Their music is fundamentally vocal and non-instrumental this makes measure of data present in open circle even less.Also local american culture has been hurt and devastated by non-locals, as America was settled essentially from European and African pilgrims
So generally we rely upon records of European Scholars with respect to the history and culture of local Americans.These European researchers had distinctive taste of music, so records of these researchers are misshaped. That is the reason it is hard for the ethnomusicologists to examine the local american music.